How do I loft lines into a mesh with Animation Nodes?
It's easier if you use an existing node to loft elements, which is the Spline Loft node instead. Basically, you create a bunch of splines before, feed that as a list to the node, and then decide on the amount of samples / divisions of the mesh. See this blend here:



Here's a screenshot of the full setup:



The loop below is a workaround for me to get a few splines in the fashion that you did. I feed a list of integers into it, only using the loop index to generate a few start and end coordinates. With that, I create straight splines and collect them in a list at the end.

This spline list I feed back into the loft node. The samples parameter determines the number of points on the spline which the node generates. Spline Samples of 2 means, only start and end point, so a straight line. Important: you also need to set the samples in the other direction. That's why I get the list length in the end, so each spline is then sampled as a division as well.

Using a bit of randomness, you get this: